As integrated circuits have continued to shrink in size, structures and materials that once were adequate for certain purposes, have become inadequate for their designated purposes. As the term is used herein, “integrated circuit” includes devices such as those formed on monolithic semiconducting substrates, such as those formed of group IV materials like silicon or germanium, or group III-V compounds like gallium arsenide, or mixtures of such materials. The term includes all types of devices formed, such as memory and logic, and all designs of such devices, such as MOS and bipolar. The term also comprehends applications such as flat panel displays, solar cells, and charge coupled devices.
For example, the small-featured traces and other electrically conductive structures of integrated circuits need to be adequately electrically insulated one from another. As feature size has decreased, and circuit speeds have increased, the dielectric materials used for electrical isolation are not adequate for the task, and tend to exhibit capacitance and other effects between the electrically conductive features. These effects tend to induce cross-talk and slow the switching speeds of the circuits.
To resolve issues such as these, new dielectric materials with lower capacitance values—so-called low-k materials—have been used in the fabrication of integrated circuits. Unfortunately, after these materials are deposited, subsequent processing of the integrated circuit might alter the capacitance of these low-k materials. For example, the effective k value of low-k films has been observed to change after etching and ashing processes.
Capacitance is traditionally tested in a final test of electrical parameters at the end of the fabrication cycle. However, it can take up to a month or more to complete the fabrication process and perform the tests. If the issues described above in regard to effective k value or uniformity are detected, the substrates bearing the integrated circuits having the problem may need to be scrapped, possibly along with all of the other substrates that are in the line.
What is needed, therefore, is a system that overcomes problems such as those described above, at least in part.